If you insist on doing this with strings, then try this:
void currentDAY_compare() {
for (int j = 0; j < 7; j ++) {
if (strcmp(currtweekDAY[0], SDFoldersB0[j]) == 0) {
CMDDAYmark = j;
Serial.print("100SDFoldersB0[j] =");
Serial.println(SDFoldersB0[j]);
Serial.print("103 j =");
Serial.println(j);
}
}
}
Although it is much simpler to just do something like this:
void printLocalTime() {
struct tm timeinfo;
if (!getLocalTime(&timeinfo)) {
Serial.println("Failed to obtain time");
return;
}
Serial.print("numeric day of week: ");
Serial.println(((timeinfo.tm_wday) + 6) % 7); //convert start of week from Sunday to Monday
Serial.println(&timeinfo, "%A, %B %d %Y %H:%M:%S");
}